The main objective of this research is to examine the impact of stress and social support on the occurrence of depressive symptoms and major depressive disorder. The focus is on assessing intraethnic variation among Mexican Americans and interethnic variation between this group and non-Hispanic whites. This research is significant because depression is among the most prevalent mental disorders, but etiological factors among Mexican Americans have not been extensively studied in previous research. A series of analyses based on the existing three-wave panel data collected at the UCLA site of the Epidemiologic Catchment Area Program (LA-ECA) will be conducted. These data were collected with three interviews conducted with the same individuals at six month intervals. Data collection began in 1983 and ended in 1985. The data are from a community-based probability sample of Mexican Americans (N=1,244), non-Hispanic whites (n=1,310), and other racial-ethnic groups (N=578). Of the 3,132 persons intially interviewed, 2,040 and 2,406 were reinterviewed at the 6-month and 1-year follow-ups, respectively. The Diagnostic Interview Schedule (DIS) was used to collect the information necessary to generate diagnoses of major mental disorders according to DSM- III criteria. Depressive symptoms were also assessed with the Center for Epidemiologic Studies-Depression (CES-D) scale. Life event stress, role strains, social relationships, and perceived socioemotional support were also ascertained. The proposed longitudinal analysis will examine first intraethnic variation among Mexican Americans and non-Hispanic whites in exposure to stress, the presence of social support and level of depression. A model of the extent of which social support lessens or buffers the impact of stress on subsequent depression will be tested within both ethnic groups. Interethnic differences in these variables and their interrelationships will then be assessed. Within the Mexican American group, the effets of immigrant status and level of acculturation will also be examined. This research will additionally examine the extent to which the same etiological models apply to depressive symptoms and major depressive disorder. Finally, the extent of which stress and social support affect the occurrence of phychiatric disorder other than depression will be explored.